This invention relates to a method and apparatus for the sequential handling of a series of individual flexible products, and more particularly to a high speed handling and delivery system for flexible plastic bags or containers.
In the production of individual flexible web products such as plastic containers and bags, the bag stock is typically supplied in the form of a continuous web of thermoplastic material which has been folded upon itself to form two plies. In forming individual bags, portions of the thermoplastic material are severed from the web. These severed areas become side seams for the bags and are typically sealed at the same time as they are severed by the use of a heated wire element. The bags are then stacked, counted, and packaged by packing equipment.
The severing and sealing operation typically takes place on a relatively large diameter rotating drum which may contain multiple heated wire severing and sealing elements positioned in grooves located within the outer periphery of the drum. As the drum rotates, different severing and sealing elements are actuated to raise them up to the drum surface to sever and seal a respective portion of the bag stock web. The individual bags are retained on the drum by a vacuum arrangement as the drum rotates. Such drums are large and expensive pieces of equipment. However, they can presently be operated at production speeds in excess of the production speed of the packaging equipment. Present commercial drums are capable of operating simultaneously on a pair of bag webs positioned side-by-side on the drum.
Individual bags are then taken from the drum, stacked, and packaged. Desirably, the packaging operation occurs at the highest possible speed the equipment can be operated to increase productivity of the system. Presently, individual bags are taken from the drum by a smaller transfer drum, also suitably equipped with vacuum capabilities. The vacuum on the bags on the large drum is relieved at an appropriate point, and the bags fall onto the smaller drum where they are held in position by vacuum. At an appropriate point, the vacuum is released and the individual bags are pulled off the smaller drum by an orbital packer or similar device. Again, present commercial equipment is designed to remove side-by-side pairs of bags simultaneously and package those bags with separate pieces of packaging equipment.
As is conventional, the orbital packing device is provided with a set of packer fingers which move in a circular path in precise timing with the smaller drum so that the fingers remove successive bags, which are typically separated on the drum approximately a nominal 1/8 inch from each other, from the drum and stack them on a stacking table against a backstop. These orbiting packer fingers must move at very high speeds to strip each successive bag from the drum and may actually accelerate the bags toward the backstop. Such acceleration of the bags is undesirable as the bags may bounce or crumple when they hit the backstop. This leads to machine jams, causing excessive downtime for the machinery.
Even if the machinery does not jam, the stack of bags which is formed on the stacking table may be uneven so that when the stack is boxed, bags may be left hanging out of the box. Such boxes must be removed from the assembly line and repacked by hand. Even minor unevenness of the bag stack may make it more difficult for a consumer to dispense the bags from a box. If one or more of the bags in the stack is crumpled, the vertical height of the stack is affected so that when the count fingers are activated to separate the previous precounted stack from the next stack, the fingers may strike the stack. Again, this leads to machine jams and downtime for the machinery.
Another problem in conventional orbital packing devices is that the packer fingers contact substantially less than the full bag width as they move out of the grooves and strip the bag from the surface of the transfer drum. At typical operating speeds, the stingers accelerate the bags vertically downwardly away from the transfer drum surface at a high velocity. In some instances, this may cause the trailing edge of a bag, which is not in contact with the packer fingers, to fold up and over against itself. Longer packer fingers which would extend across the entire width of the bag are not possible in conventional equipment as the fingers would tend to contact the leading edge of the next succeeding bag on the drum. A folded bag placed on the bag stack again affects the height of the stack so that the count fingers may not operate properly to remove the stack from the stacking table. Additionally, such a folded bag may also cause a jam from the next bag striking the folded trailing edge.
Both the orbiting packer fingers as well as the count fingers are subjected to high inertial forces. After a predetermined number of bags have been removed, count fingers or other suitable separation means are actuated to separate the continuous stream of individual bags into precounted stacks. To accomplish this, the count fingers must move from a first position fully out of the stream of bags, to a second position fully in the stream. This movement must be accomplished in the fraction of a second between successive bags as they are delivered from the smaller drum. At high production rates, this time can be less than 0.1 seconds. This results in the production of tremendous acceleration forces on the count fingers as high as 30 times the force of gravity. High inertial forces also affect the remainder of the packaging system for the folding and loading of the product into dispensers. Thus, operation at the design limits of the packing equipment results in high inertial loading which is detrimental to machinery life and results in excessive downtime and maintenance costs.
Attempts have been made in the past to increase the production rates of packing systems by providing multiple lane stacking systems for relatively thick and/or stiff products such as diapers (Campbell, U.S. Pat. No. 4,523,671) and slices of wrapped cheese or meat (Driessen, U.S. Pat. No. 3,683,730). Both Campbell and Driessen teach systems for the side shifting of individual items from a single path to a plurality of paths. However, such systems were not designed for the stacking of relatively thin, flexible products such as plastic bags which may become folded over and cause machine jams.
Accordingly, it would be desirable to be able to utilize the capability of the product drum to produce products at the higher rates that it is capable of and yet maintain or even increase the higher production rates without subjecting the packaging system to such high inertial forces. The need still exists in the art for such a high speed product handling and delivery system and method for handling relatively thin, flexible products such as plastic bags.